Question

A white-eyed Drosophila is mated with a red-eyed (wild-type) male, the reciprocal cross of the one shown in Fig 15.4. What phenotypes and genotypes do you predict for the offspring from this cross?

Short answer

The genotype of female offspring would be X^w+X^w, and male offspring would be X^wY.

The phenotype of females would be red eye color, and males would be white eye color.

Step-by-step solution

Sex chromosomes of Drosophila

Fruit flypossesses one pair of sex chromosomes.Female fruit flies have two X chromosomes, whereas males have one each of the X and Y chromosomes.

The gene for the eye color of Drosophila is located on the X-chromosome. The wild eye color of the fly is red, but the mutant phenotype is white. However, the white eye color of Drosophila is recessive.

The genotype of the parents

The allele for wild-type trait (red color) is w⁺, and the allele for non-wild type trait (white color) is w. Thus,the genotype of a white-eyed female would be X^w+X^w+ because white eye color is recessive and manifests itself when both the mutant alleles are present. The genotype of a red-eyed male would be X^wY as it has wild eye color.

When a white-eyed female (X^w+X^w+) is crossed with a red-eyed male (X^wY), the phenotype of offspring can be determined from the genotype of the offspring.

Phenotype and genotype of the offspring

The genotype of the female offspring would be X^w+X^wbecause all the female offspring would receive one non-wild type allele from the female parent and one wild type allele from the male parent. Thus,all the female offspring would be heterozygous with red eye color.

The genotype of the male offspring would be X^wY because all the male offspring would receive a Y chromosome from the male parent and a non-wild type allele from the female parent. Thus,all the male offspring would be white-eyed.

Thus, half of the offspring would be red-eyed females, and another half would be white-eyed males.